German investigators identified the Tunisian man who killed 12 people in Berlin before Christmas as a threat in February last year but decided it was unlikely he would carry out an attack, the Sueddeutsche Zeitung reported.

Anis Amri, 24, plowed a truck through a Berlin Christmas market on December 19. Islamic State claimed responsibility for the attack, calling the assailant a “soldier” of the militant group.

The German authorities had determined Amri posed a threat after receiving intelligence showing that in early February he had been in contact with suspected members of Islamic State and offered himself as a suicide bomber, the Sueddeutsche reported.

Officials at the German Interior Ministry were not immediately available for comment.

Amri, whom Italian police shot dead in Milan on December 23, had wanted to acquire weapons for an attack in Germany and sought accomplices, the Sueddeutsche said in a joint report with German broadcasters NDR and WDR, citing security documents.

However, German officials who subsequently met to decide whether to deport Amri, determined he posed no acute threat that could be presented in court.

Amri's attack in Berlin has prompted German lawmakers to call for tougher security measures. In a New Year's address to the nation, Chancellor Angela Merkel said Islamist terrorism is the biggest test facing Germany.